This project is a continuation of research supported in part by EY--405 (and earlier USPHS grants) under the title "Information channeling in the retina". Because recent progress has resulted in some shifts in scope and emphasis a different title has been used for this proposal "Sensory mechanisms in visual orientation". Its primary objective is to study visual information processing with relevance to spatial orientation. Particular emphasis is placed on the mechanism of polarized light sensitivity and the channeling of the resulting information (1) with relation to other visual parameters like wavelength and (2) with relation to the resulting oriented behavior (polarotaxis). While the experimental organisms have been higher invertebrates (mainly crustaceans but also occasional cephalopods and insects) and lower vertebrates (fishes) the results are relevant to several basic areas of broad importance: (1) relation between fine structure and function in photoreceptors (2) sensory integration of various light stimulus dimensions, and (3) control of simple aspects of spatial orientation by visual inputs. Specifically these general objectives are being pursued in two different but related programs: (1) Analysis of the functional significance of receptor fine structure in compound eyes of crustaceans. (2) Study of the occurrence and mechanism of polarized light perception in fishes. A wide range of techniques and experimental methods are being employed ranging from electron microscopy to intracellular recordings and the use of phototactic and polarotactic behavioral responses.